Torque limited drive for manual valves

ABSTRACT

The present invention is directed to a torque-limiting handwheel device for preventing manual valves from being damaged due to the application of excessive torque during the opening or closing operation of the valves. Torque can only be applied when ridges in the handwheel assembly engage in channels machined in the face of the baseplate. The amount of torque required for disengagement of the ridges from the channels is determined by the force exerted by various Bellville springs and the inclination of the side faces of the channels.

This invention was made as a result of the work done under contractDE-AC05-840R21400 with Martin Marietta Energy Systems, Inc., and theU.S. Department of Energy.

BACKGROUND OF THE INVENTION

The present invention relates generally to a torque limiting handwheelfor preventing manual valves from being damaged because of the excessiveapplication of torque during the opening and closing operation of thevalves.

Because of the variety (manufacturer and size) of valves, it isdifficult for operators to keep up with the torque limits of eachparticular valve. The application of excessive torque has been the causeof many valve failures. Operator judgment becomes a frequent substitutefor a torque wrench. When excessive valve seat leakage occurs, it is anatural tendency to apply excessive torque to the valve to correct thevalve seat leakage. It is costly and time consuming to replace thedamaged valve seats due to excessive torquing by the operators.

It is, accordingly, a general object of this invention to develop atorque-limiting handwheel which when installed on a valve, prevents thevalve from being damaged through the application of excessive torqueduring operation of the valve.

Another more particular object of the invention is to provide atorque-limiting handwheel wherein an almost infinite range of maximumtorque levels may be achieved.

Yet another object of the invention is to provide a torque-limitingdevice for manual valves wherein a common set of hardware canaccommodate a wide range of valves having different allowable operatingtorques.

Another object of the invention was to devise a torque limiting featurefor manual valves which can be applied as an integral part of a valvehandwheel, the valve lazy rod, separate from the valve or beincorporated into a valve wrench.

SUMMARY OF THE INVENTION

A torque-limiting drive for preventing manual valves from being damageddue to the application of excessive torque during the opening or closingoperation of the valves is provided in accordance with this invention.The torque-limiting device comprises a base plate member having channelsradially disposed on its upper surface from a central bore. A handwheelmember with ridges radially disposed on its lower surface atcorresponding radial positions respectively engage and disengage theaforesaid channels to limit the torque on the device. Torque can only beapplied when the ridges in the handwheel assembly are engaged in thechannels machined in the baseplate of the device. Compression of variousBellville springs, and the inclination of the engaging side surfaces ofthe respective ridges and channels determine the amount of torque whichwill cause disengagement of the ridges from the channels. Therefore,valve torque limits can be adjusted with a single set of hardware bysimply adjusting the compression of the Bellville springs.

It is, accordingly, a general object of the invention to provide atorque-limiting handwheel which when installed on valves, prevents thevalves from being damaged by the application of excessive torque duringthe valve operation.

Other and further objects will be obvious upon an examination of theillustrative embodiment about to be described or will be indicated inthe appended claims, and various advantages not referred to herein willoccur to one skilled in the art upon employment of the invention inpractice.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded isometric view showing the torque-limiting fixturein accordance with the present invention.

FIG. 2 is an assembled side view of the torque-limiting fixture.

DETAILED DESCRIPTION OF THE INVENTION

As briefly mentioned above, the present invention is directed toproviding a torque-limiting handwheel device for preventing manualvalves from being damaged by an excessive application of torque duringthe opening and closing operation of the valves. The torque-limitingdevice consists of a valve assembly with a steel baseplate havingradially disposed channels or grooves on its upper surface and ahandwheel member with ridges on its lower surface that respectivelyengage and disengage the channels to limit the torque on the device.

Described in general detail and with reference to the accompanyingdrawings, the torque-limiting device assembly is shown at 10 in FIG. 1where it is used in conjunction with a valve assembly 12 having athreaded valve stem 14. Threaded valve stem 14 accommodates a heattreated baseplate member 16 having channels or grooves 18 radiallydisposed at 120° intervals from central bore 20, on its upper surface22.

Handle wheel assembly 24, includes an upper plate 26 defining ridges 28on its lower surface 30, which are radially disposed from central bore32 at 120° intervals so as to engage channels 18 in baseplate member 16when the handle assembly is being operated within its torque limits.Handle 34 attached to upper plate 26 allows for a rotating movement ofplate 26 about stem 14 during opening or closing of valve assembly 12.As shown, handle wheel assembly 24 further includes spacer 36, aplurality of Bellville springs 38, 38', 38" and spacers 40-40' disposedcoaxially on threaded valve stem 14. Nut 42 on threaded valve stem 14completes the assembly.

In operation, valve assembly 12 with threaded valve stem 14 beingcentrally disposed and fixably attached to baseplate 16, along withhandwheel assembly 24, which is rotatably supported on valve stem 14,allows member 24 to rotate independently about threaded valve stem 14when the torque limits of the subject device are exceeded and ridges 28are disengaged from channels 18. The interface of surfaces 22 and 30 areprovided with a grease lubricant to improve the repeatability of themaximum torque levels achieved during cyclic functioning of the device.

The amount of torque required to release baseplate 16 from handwheelassembly 24 is a function of the forces applied to members 16 and 24 bythe plurality of stacked Bellville springs 38-38'-38" and washers 40 and40' and the inclination of the slopng side surfaces of channels 18 andridges 28.

In the preferred embodiment, channels 18 in surface 22 of baseplate 16have a depth of 0.10-inch, a top width of 0.20-inch, tapering downwardat a 45° angle to a bottom width of 0.10-inch. Ridges 28 in handwheelassembly 26 thus are machined correspondingly to mate with channels 12.

A wide range of torque levels is achievable within the limits imposed bythe strength of materials from which the device is fabricated.Variations in torque-resistance or resilience are obtained initially byselecting the angle of the incline of the side surfaces channels 18 andridges 28 by which the two main members, baseplate 16 and handwheelassembly 24 are engaged with smaller singles providing lower torquelimits.

The effect on torque (in./lbs.) of increasing the number of washers 40between Bellville springs to increase the spring compression can be seenin table 1 where, in a typical test, 25 data points for each variationwas made. The effect of changing the number of spacing washers 40 is toincrease or decrease the deflection of the Bellville springs, therebyproviding an increase or decrease in the force driving baseplate 16 andupper plate 26 together. Larger forces between plates 16 and 26 willprovide a corresponding increase in the torque needed to cause relativerotation of those plates due to the engagement of ridges 28 in grooves18 with greater force will be more resistant to disengagement.

                  TABLE I                                                         ______________________________________                                        Torque (in/lbs) for Washers, number                                           Data                                                                          Points  0       1      2     3    4     5    6                                ______________________________________                                                115     127    130   167  177   216  228                                      103     112    152   149  176   193  211                                      110     134    144   145  179   184  198                                      110     123    135   161  171   196  218                               5      112     115    150   147  179   201  208                                      100     128    145   164  174   184  210                                      112     122    147   159  183   193  206                                      113     113    145   150  177   199  208                                       98     132    132   166  166   183  201                              10      115     123    145   155  177   196  211                                      105     113    140   142  169   196  210                                       96     128    134   164  167   184  198                                      110     117    142   154  177   198  211                                      103     112    132   145  177   191  208                              15       96     130    149   162  167   186  203                                      112     120    144   159  177   198  210                                      101     113    132   144  177   199  208                                       95     130    149   161  167   184  203                                      110     120    144   162  176   198  211                              20      105     113    127   152  174   199  208                                      100     127    152   164  166   184  199                                      108     113    144   162  176   199  208                                      103     128    135   147  174   188  204                                      100     123    149   161  167   181  199                              25      108     127    145   161  176   183  210                              Average 106     121    142   156  174   193  207                              ______________________________________                                    

Torque was measured electronically utilizing strain gages affixed to asimulated valve stem and calibrated to cover the range of 0 to 2400 in.lbs. Increasing the numbers of 0.010 washer results in a generallylinear increase in torque from 106 in. lbs. to 207 in. lbs. for a caseusing the 0.047-in Bellville springs.

Turning to Table II, estimated torques are given for the inventionwherein three Bellville springs are used in combination with variousnumbers of washers. Using three types of Bellville springs (Type I=0.047-inch, Type II=0.087-inch, Type III=0.112-inch) and the indicatednumber of washers, maximum operating torques of from 33-2100 in. lbs.are achievable.

                  TABLE II                                                        ______________________________________                                        Torques achievable                                                            with this device,                                                                           Three Bellville                                                                           0.010 Washers,                                      inch-pounds   Springs, Type                                                                             Quantity                                            ______________________________________                                         33           I           0                                                    61           I           1                                                    89           I           2                                                   100           II          0                                                   116           I           3                                                   144           I           4                                                   172           I           5                                                   200           I           6                                                   300           II          1                                                   350           III         0                                                   500           II          2                                                   700           III         1                                                   700           II          3                                                   900           II          4                                                   1050          III         2                                                   1100          II          5                                                   1400          III         3                                                   1750          III         4                                                   2100          III         5                                                   ______________________________________                                    

On the basis of this data it is now possible to utilize a common set ofhardware to accommodate a plurality of commercial valves having a widerange of allowable operating torques. Thus, by varying spacer thicknessand/or number; varying Bellville spring thickness and/or number; or byvarying the Bellville spring arrangement, all within a constant space, apredetermined and precise torque can be supplied for any givenapplication.

The foregoing description of a preferred embodiment of the invention hasbeen presented for purposes of illustration and description and is notintended to be exhaustive or to limit the invention to the precise formdisclosed. It was chosen and described in order to best explain theprinciples of the invention and their practical application to therebyenable others skilled in the art to best utilize the invention invarious embodiments and with various modifications as are suited to theparticular use contemplated. For example, further variations in torqueresistance or resilience may be obtained by varying the angle of theincline of the channels and ridges by which the two main members areengaged. One skilled in the art will also recognize that it is nowpossible to utilize a common set of hardware to accommodate a pluralityof commercial valves having a wide range of allowable operating torques.It will also be recognized that a variation in torque limit can beachieved without the use of different numbers of spacer washers bysimply advancing or withdrawing nut 42 along the threaded end of stem 14to effect a greater or lesser compression of the Bellville springs 38.Calibrating marks could be provided on stem 14 to indicate the axialposition of nut 42 and the torque limit associated with that position.It is intended that the scope of the invention be defined by the claimsappended hereto.

We claim:
 1. In a manually operated valve assembly including a rotatablevalve stem for opening and closing the valve assembly, the improvementcomprising a torque-limiting handwheel for preventing damage to saidvalve assembly caused by the excessive application of torque to saidstem, said handwheel comprising:a first plate fixably attached to saidstem and rotatable therewith, said first plate having a generally planarsurface disposed orthagonal to the longitudinal axis of said stem anddefining at least one radially extending groove; a second platerotatably attached to said stem having a generally planar surfacedisposed orthagonal to the longitudinal axis of said stem and definingat least one radially extending ridge shaped to mate with said groove insaid first plate, said planer surfaces in said first and second platesbeing disposed in a continuous manner with said ridge and channels insaid respective plates being engaged when said valve is operating withindefined torque limits; means for manually imparting torque to saidsecond plate to rotate said second plate during valve operation; meansurging said first and second plates together to maintain said ridge andgrove in mating relationships during normal valve operation.
 2. Theimprovement of claim 1 wherein there are three radially extendinggrooves spaced 120° apart in said first plate and three radiallyextending ridges spaced 120° apart in said second plate.
 3. Theimprovement of claim 1 wherein said means for urging said first andsecond plate together comprises at least one Bellville spring disposedon said stem and means compressively securing and spring against saidsecond plate to force said second plate against said first plate.
 4. Theimprovement of claim 3 further including at least one spacer washermounted on said shaft to maintain a selected level of compression ofsaid Bellville spring.